Modulation is the process in which high frequency carrier wave parameters are altered corresponding to changes in a lower frequency data signal. It is obvious that using a carrier signal in the optical frequency range increases the bandwidth usage and decreases the size of elements. So it can increase the volume of data transmission in optical fibers. Modulator role in this system is reshaping of information (in the form of digital or analog) signal from a continuous wave laser of LED source. Optical modulator as one of the main components in optical communication systems can be divided in two types of external and internal (direct) modulators. Due to devastating effects and restrictions like chirp effect in the internal modulators, external modulators are used for large distances. This kind of modulators is based on the electro-optic and magneto-optic effects. Evaluation and comparison of different types of external modulators are discussed in this thesis. Also the waveguide photonics crystal modulators are introduced and simulated and some proposals for the improvement of their structures are mentioned. Keyword: polarization, External modulator, Anisotropic medium , Electro-optic and Magneto-optic effects, Photonic crystal.
